tpl: Modified error messages of after, first, and last

Modified the messages functions after, first, and last threw on being passed invalid parameters (index or limit) to be more standardised and resemble what Go compiler would throw.

Fixes gohugoio#6415

tpl/collections/collections.go

@@ -61,7 +61,7 @@ func (ns *Namespace) After(index interface{}, seq interface{}) (interface{}, err
 	}
 
 	if indexv < 0 {
-		return nil, errors.New("can't return negative/empty count of items from sequence")
+		return nil, errors.New("sequence bounds out of range [" + cast.ToString(indexv) + ":]")
 	}
 
 	seqv := reflect.ValueOf(seq)
@@ -219,7 +219,7 @@ func (ns *Namespace) First(limit interface{}, seq interface{}) (interface{}, err
 	}
 
 	if limitv < 0 {
-		return nil, errors.New("can't return negative count of items from sequence")
+		return nil, errors.New("sequence length must be non-negative")
 	}
 
 	seqv := reflect.ValueOf(seq)
@@ -379,7 +379,7 @@ func (ns *Namespace) Last(limit interface{}, seq interface{}) (interface{}, erro
 	}
 
 	if limitv < 0 {
-		return nil, errors.New("can't return negative/empty count of items from sequence")
+		return nil, errors.New("sequence length must be non-negative")
 	}
 
 	seqv := reflect.ValueOf(seq)